The present invention relates to fuel vapor venting during refueling of a motor vehicle fuel tank from a discharge nozzle placed into a tank filler tube of the type having a mechanical seal about the nozzle. Present fuel tank refueling nozzles commonly include a vacuum actuated device which shuts off the nozzle upon starvation of the vent vapor recirculation line thereby creating a vacuum in the filler tube around the nozzle.
Heretofore, in filler tubes not having a mechanical seal about the nozzle, the fuel tank vapor system provided for recirculation of the fuel vapor to the filler tube by connection to the vent line to the system vapor storage canister. In other known systems the system storage canister is connected to a separate vent tap through the top wall of the tank with a rollover valve for preventing spill leakage of fuel. The system employing the recirculation vent tap into the line to the canister must therefore rely upon the float operated fuel vapor vent valve in the tank to shut off the vent line when the fuel level has reached the top of the tank causing liquid to back up into the filler neck and shut off the nozzle. Such float operated vent valves are critical in their calibration in order to provide proper vapor venting as fuel is introduced into the tank and also must reliably close in the event of vehicle rollover. Heretofore, both of these latter requirements have been the source of problems in vehicle service for such float operated valves.
The type of system employing a vapor recirculation vent tube directly from the tank top to the upper end of the filler tube relies upon the liquid fuel covering the end of the tube through the top of the tank in order to starve vapor recirculation to the upper end of the filler tube thereby creating a vacuum for nozzle shutoff.
Referring to FIG. 4, a known system is illustrated wherein the fuel tank 1 has a float operated vent valve 2 mounted in the upper wall of the tank with the vent outlet thereof connected to the inlet of an electrically operated purge valve 3 which is controlled by an electronic controller or ECU 4. The outlet of the vent valve 2 is also connected to the inlet of a storage reservoir or canister 5. A recirculation port 6 in the upper end 7 of a filler tube 8 is provided for fuel vapor recirculation to the upper end of the filler tube during refueling by the nozzle discharging into the filler tube.
A recirculation vent line 10 is connected to the top of the tank to provide fuel vapor recirculation to the port 6 in the upper end of the fill tube 7 during refueling independently of the float operated vent valve 2 in which case a separate rollover spill protection valve 11 may be employed. In this latter arrangement the end of the tube extends through the upper tank wall to the desired level for having the liquid fuel close the end of the tube and terminate vapor recirculation to the fill tube end 7 when the fuel reaches a predetermined level. Typically, the recirculation line 10 must be routed along the top of the tank over the edge and along the filler to facilitate installation in the vehicle.
In the prior art system requiring a separate vent tube from the tank top to the upper filler neck, careful placement of the end of the vent tube in the tank is required to effect closing of the end of the vent tube at the desired fuel level in order to prevent liquid fuel backup in the filler tube. Furthermore, the routing of the recirculation line creates a liquid trap in the line, which can block recirculation and cause undesired vacuum in the filler tube during refueling and activation of the automatic nozzle shutoff.
Accordingly, it has been desired to provide a more positive way or means of cutting off vapor vent recirculation to the upper end of the filler tube during refueling when the liquid fuel level has risen to the desired full position.